Manufacture of a strip by extrusion of a tube then flattening the tube

ABSTRACT

A process and apparatus for laying a strip for the manufacture of a tire by extruding uncured rubber through a die to form a rubber tube on a rotary support and flattening the tubular form to form a band which is adhered to a receiving surface on the rotary support.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a divisional of U.S. patent application Ser. No.09/978,451, filed Oct. 17, 2001, now U.S. Pat. No. 6,666,940, issuedDec. 23, 2003, which claims priority to French Application No. FR00/13424, filed Oct. 18, 2000.

BACKGROUND OF THE INVENTION

The present invention relates to the laying of rubber products for themanufacture of tires. More precisely, the present invention relates tothe manufacture of a tire by winding strips and it relates to themanufacture of semi-finished products in the form of strips.

It is already known that, in order to manufacture a tire of uncuredrubber, the laying of all or part of the rubber products may be effectedby winding a strip on a manufacturing support. For example, patentapplication EP 0 264 600 proposes using extrusion of the volumetric typefor laying the rubber products with great accuracy. Patent applicationEP 0 690 229 proposes a volumetric pump used for continuously extrudinga strip of uncured rubber with great accuracy.

One well-known problem in the tire industry is that somesulfur-vulcanizable rubber mixes are quite difficult to extrude: the mixhas a tendency to crumble, and does not have a smooth surface downstreamof the extrusion but rather a granular, bumpy, rough surface whichsometimes contains incipient tears. It is difficult to impart an exact,regular form such as a strip to such mixes. This involves difficultiesin handling the extruded semi-finished products. This also involvesdifficulties in laying such products on a raw tire blank duringmanufacture because the adhesion of such mixes in the uncured state isgenerally poor.

This is particularly difficult in the technique of winding a strip on asupport because, in this case, the extruded rubber sections are quiteweak and it is important to be able to extrude strips at high speed inorder to be able to lay the necessary volumes of rubber within asuitable time. Now, generally, for a given mix formulation, the more therate of extrusion and/or of winding on a support is increased, the morethe difficulties increase.

SUMMARY OF THE INVENTION

The invention proposes forming a strip by first manufacturing a tubewhich is subsequently flattened.

A first aspect of the invention relates to the laying of a componentcomprising uncured rubber during the manufacture of a tire, the layingbeing effected by winding a band on a rotary support having a receivingsurface, by a process comprising the following stages:

-   -   extruding uncured rubber through a die imparting a tubular        section to the extruded uncured rubber to form a rubber tube,        the wall of which defines an internal cavity,    -   flattening the tubular form and thus obtaining a band which is        adhered to said receiving surface.

A second aspect of the invention relates to the manufacture of a band ofuncured rubber, with addition of a component to the band downstream ofan extrusion operation. This may consist of adding fibers. It mayconsist of adding an additive, in particular a material capable ofmigrating into uncured rubber. The process comprises the followingstages:

-   -   extruding uncured rubber through a die imparting a tubular        section to the extruded uncured rubber to form a tube of uncured        rubber, the wall of which defines an internal cavity,    -   concomitantly with the extrusion, introducing a material into        said tube, in a predefined amount,    -   flattening the tubular form and thus obtaining a band.

In the examples described below, a rubber tube is extruded using acylindrical die containing an ovoid which is also cylindrical and ofslightly smaller size so as to leave an air gap of revolution betweenthe nozzle and the ovoid. It goes without saying that the cylindricalshape is not limitative, and other forms may be considered, inparticular an oval section. The form of revolution is howeveradvantageous for machining parts.

In what follows, different possible applications of the invention aredescribed, in non-limitative manner, which makes it possible tounderstand the entire scope and all the advantages thereof.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section showing an extrusion head equipped with a die for afirst application of the invention.

FIG. 2 shows a diagram of an extrusion machine in cooperation with arotary core acting as a manufacturing reference for a tire, illustratingthe first application of the invention.

FIG. 3 is a partial section along III—III of FIG. 1.

FIG. 4 is a partial section along IV—IV of FIG. 1.

FIG. 5 is a partial section through a section plane containing thecentral axis of a die of revolution, showing a variant embodiment of adie in the first application of the invention.

FIG. 6 is an enlargement of part of FIG. 5.

FIG. 7 is a partial section through a section plane containing thecentral axis of a die of revolution, showing another variant embodimentof a die in the first application of the invention.

FIG. 8 is an enlargement of part of FIG. 7.

FIG. 9 shows the ovoid of FIG. 7, in isolation.

FIG. 10 shows means used for pressing a strip against the receivingsurface, in the first application of the invention.

FIG. 11 is a left-hand view of the variant embodiment illustrated inFIG. 10, some details being omitted.

FIG. 12 is a partial view along AA in FIG. 10.

FIG. 13 is a partial view along BB in FIG. 10.

FIG. 14 shows a second application of a die according to the invention.

FIG. 15 is a diagram of a strip winding made by the invention.

FIG. 16 is an enlargement of part of FIG. 15.

FIG. 17 shows another variant embodiment of a die, which can be usedequally well in the first application and in the second application ofthe invention.

FIG. 18 is an enlargement of part of FIG. 17.

FIG. 19 shows another variant in a different adjustment.

FIG. 20 is an enlargement of part of FIG. 19.

FIG. 21 is a diagram of a strip winding made by said other variant ofthe invention.

FIG. 22 is an enlargement of part of FIG. 21.

DESCRIPTION OF PREFERRED EMBODIMENTS

In FIG. 2, there can be seen a core 30 of substantially toroidal shape,constituting a reference for the manufacture of a tire. Thismanufacturing technique is known. To extrude rubber, an extruder is usedwhich is mounted on a manipulating robot which permits all the relativepositions desired between said receiving surface and the die, the latterbeing positioned opposite the receiving surface for extruding thetubular form in the vicinity of the receiving surface, the tubular formbeing flattened on the receiving surface directly after extrusion.

The invention extends to a machine for laying a component comprisinguncured rubber for the manufacture of a tire, said machine winding aband on a rotary support, said machine comprising the followingelements:

-   -   an extruder equipped with a die 1 imparting a tubular form to        the section of extruded uncured rubber,    -   a rotary support of revolution, serving as a reference for the        manufacture of the tire,    -   a manipulating robot 19 which permits all the desired relative        positions between said support of revolution and said die,    -   at least one roller 40 cooperating with the rotary support to        flatten the tubular form onto it downstream of said die.

There can be seen a pump 10 for uncured rubber constituting one possibleexample of an extruder. The pump 10 for uncured rubber is supported by amanipulating robot 19. The rubber pump comprises essentially a fillingscrew 102, one or more pistons 101 and an extrusion die 1. Starting froma band of rubber 2, the pump enables a strip 22 to be laid on thesurface S of the core 30. A roller 40 facilitates laying. Themanipulating robot 19 makes it possible to move the extrusion die Itowards or away from the core 30 along the axis X and to displace ittransversely along the axis Y, and also makes it possible to rotate therubber pump about the axis α. The axis α passes substantially throughthe point at which the strip 22 rejoins the surface S.

The machine is placed under the control of an automatic machine thatmakes it possible to drive it appropriately. By way of illustration,mention may be made of certain parameters which depend on each other andare controlled by the automatic machine: speed “V” of the screw 102,mechanically linked to the speed of operation of the piston(s) 101,effective laying radius “r” (different according to the zone of thetire—for example bead or tread—or different from one winding to theother in the case of superposition of windings to produce the tread),speed of rotation “N” of the core 30. Here a volumetric extruder isused, the flow rate of uncured rubber extruded being controlled inparticular as a function of the speed of rotation of the receivingsurface and of the radius of lay of the band.

In FIG. 1, there can be seen in greater detail a first embodiment of adie 1 according to the invention. The latter comprise a pre-die 17mounted on a rubber pump 10. The roller 40 cooperates with the core 30downstream of the extrusion orifice, which is located in the planeIV—IV. Uncured rubber 20 is delivered under pressure by the rubber pump10 and arrives at the die 1. The die 1 comprises a nozzle 11 and anovoid 12 fastened to the nozzle, and partially blocking off theextrusion orifice so as to provide an air gap 15 between the nozzle andthe ovoid, the air gap ending in an extrusion section of appropriateshape.

The rubber is extruded in the form of a tube 21. One part 210 of thetube 21 is close to the receiving surface S and another part is fartheraway therefrom. The tube 21 is flattened by the action of the roller 40cooperating with the core 30 to form a strip 22 by gluing the walls ofthe tube 21.

The ovoid 12 is extended by a tail 18, mounted in an ad hoc bore on thepre-die 17, and held by a nut 180 which prevents expulsion of the ovoid12 under the effect of the delivery pressure of the rubber. Ventingmeans for the gases enclosed in the tube 21 may possibly be provided. Tothis end, the tail 18 comprises a pipe 13 that ends in a connector 14 towhich an appropriate tube can easily be connected. The pipe 13 passesthrough the ovoid 12 and opens into the extrusion orifice. The ventingmay possibly be assisted by a reduced pressure. However, the venting isnot indispensable because there is no accumulation of gas during theoperation of the invention.

The ovoid 12 advantageously comprises radial wings 121 (see FIG. 3)which center the ovoid 12 within the nozzle 11. In a variant, theposition of the ovoid within the nozzle could be adjustable between acentered position and eccentric positions, which may promotenon-axisymmetrical extrusion of the tube 21.

It can be seen in FIG. 1 that the ovoid 12 forms with the nozzle 11 acombining cone up to the extrusion orifice. In other words, the air gap15 is of minimum size at the extrusion orifice (see also 150A in FIG.6).

The dies proposed by the present invention can be adapted very easily todifferent sizes of strips that have to be produced. It is not alwayspossible to act on the control of the extrusion in order to move from asmall strip to a larger strip. In the variants shown in FIGS. 5 to 9,the extrusion die can very easily be replaced because it is mounted bymeans of a ring 16 on the pre-die 17 and is accessible from the side ofthe extrusion orifice. It is very easily possible, by unscrewing thecollar 16, to replace the assembly consisting of the nozzle 11 and theovoid 12A or 12B.

During the extrusion operations for uncured rubber, it is well knownthat sometimes more solid bodies or rubber bodies which may haveundergone initial vulcanization are included. This is why filters arefrequently provided upstream of the extrusion orifice. The disadvantageof such filters is that they introduce a high loss of pressure. In thevariant embodiment shown in FIGS. 7, 8 and 9, it is proposedadvantageously to have the minimum value of the air gap 150B upstream ofthe extrusion orifice. In this manner, if any solid body were to becomestuck at the air gap 150B, the uncured rubber which passes beyond theair gap 150B is able to form a continuous ring again before reaching theextrusion orifice proper. This arrangement acts like a filter, but witha far lower loss of pressure.

It can be seen in detail in FIG. 8 that the ovoid comprises a ringforming a boss 120 upstream of the end which is level with the extrusionorifice. Furthermore, the ovoid 12B comprises, as already indicated,wings 121 which enable it to be centered. The distance between the boss120 and the extrusion orifice is sufficient for a continuous ring tore-form downstream of any impurity blocked at the air gap 150B; whichcan be determined experimentally if needed.

Among the advantages of the invention, we may mention that thisextrusion technique does not have an edge effect. The strips thusproduced are less susceptible to the tearing which often begins at oneedge. This is very particularly advantageous for certain rubber mixes.Furthermore, owing to the use of the invention, a good quality of thestate of the inner and outer surface of the tube 21 is maintained, whichis a guarantee of good adhesive power in the uncured state of the stripthen formed by flattening.

FIGS. 10 and 11 illustrate in greater detail a rolling operation whichcan be effected downstream of the extrusion orifice proper. There can beseen the core 30 and the receiving surface S. There can also be seen thedie 1, comprising a nozzle 11 within which there is mounted an ovoid 12.A roller 40 is mounted on a fork 45 which itself is supported by an arm46 articulated to a support 44. The support 44 is integral with therubber pump 10. A spring 42 acts between the support 44 and the roller40. The roller 40 thus exerts a controlled pressure towards the core 30.There can also be seen two auxiliary rollers 41 each mounted on a sideplate 48. Each of the side plates 48 is mounted on an arm 47, which isarticulated to the support 44. Springs 43 act between each of the arms47 and the support 44, for a function comparable to that of the spring42.

It is in fact advantageous to have good rolling, effected here by threeindependent rollers, namely the roller 40 and auxiliary rollers 41,applying substantially radial forces, of a well-controlled intensitywhich is chosen by experiment, and is possibly adjustable. It isadvantageous to have springs of great flexibility in order to exert arolling stress which is substantially constant, even in the case of aneccentricity or a local imperfection in the laying of the rubber. Theroller 40 effects a first squashing of the tube 21 which has just beenextruded by the die 1, which positions the median part of the strip 22on and adheres it to the receiving surface S. The auxiliary rollers 41flatten the edges of the strip 22 on to the receiving surface S.

FIGS. 12 and 13 enable one advantage of the invention to be understood.For different reasons, among which we may mention the great accuracy oflaying of the rubber, it is desirable for the head of the rubber pump 10to be positioned as close as possible to the point at which it isdesired to lay the rubber on the tire blank being manufactured. However,the extruders used for laying strips of rubber are relativelyvoluminous. As the section conventionally extruded is rectangular, inconventional devices, the die which makes it possible to profile thetire strip has a bulk which is necessarily greater than the section ofthe strip of rubber which it is desired to lay.

The invention therefore proposes an extrusion die which is narrower thanthe strip to be extruded. Referring to FIGS. 12 and 13, it can be seenthat there is a change from a tube 21 of a given diameter “d” to a strip22, the width “L” of which is greater than the diameter of the tube 21,and is substantially comparable to the bulk “E” of the die 1.

Furthermore, it is desirable for the pattern of laying of the strips torespect as far as possible the molding shape of the tire. For example,for some treads, it is desired for the overall section of uncured rubberto approach as closely as possible the final tread pattern of the tire,to avoid or restrict the movements of rubber during molding. One is thusled, for example, to lay stacks of bands to form circumferential ribsseparated by small grooves. The problem which arises is that the head ofthe rubber pump 10, that is to say the die which profiles the rubber, byreason of its bulk, may strike the uncured rubber which has been laid toform the circumferentially adjacent rib.

FIG. 12 is a view in the direction of the arrows AA in FIG. 10, theroller 40 not being shown. There can be seen the nozzle 11 by means ofwhich a tube of uncured rubber is extruded. The tube 21 is transformedinto a strip 22 by flattening. As has already been emphasized, the strip22 is of a width “L” greater than the diameter “d” of the tube 21. Owingto the invention, it can be seen that it is possible to lay, on a tireblank 50 which is being manufactured, strips 22 to form by superpositionrubber ribs 51 without being hindered by the stacks produced at anoffset transverse position. FIG. 13 is a view in the direction of thearrows BB in FIG. 10. It makes it possible to understand that even therolling device with three rollers 40 and 41 proposed by the invention isof a bulk close to the width of the strip 22. The rolling carriage(bearing the rollers 40 and 41) easily penetrates between the cords ofuncured rubber.

Other applications of the invention are possible. It is possible toconceive of injecting another product such as, for example, avulcanization system, or reinforcement fibers into the volume enclosedin the tube 21.

FIG. 14 illustrates an application of the invention to the addition of aconstituent into the tube 21, so as to finish off the vulcanizablerubber composition. This may be, for example, the vulcanization systemand/or any appropriate additive. It is known that some constituents maymigrate into the uncured rubber, so that such an addition is notincompatible with good homogeneity. This addition is made at the time oflaying of the strip 22, in a process of laying a component comprisinguncured rubber during the manufacture of a tire, the laying beingeffected by winding a band on to a rotary support having a receivingsurface S, the band being manufactured as indicated above. However, itis possible to conceive of making a semi-finished product in thismanner.

It can be seen that the die 1B comprises a nozzle 11B and an ovoid 12B.The ovoid 112B comprises a pipe 13B which passes through the ovoid 12Band opens into the extrusion orifice. Appropriate means make it possibleto introduce a material 23 into the tube 21. A certain quantity ofmaterial 23 is thus added continuously to the uncured rubber at the sametime as a strip 22 is formed and is applied to the manufacturing support30. The automatic machine for controlling the machine according to theinvention of course ensures that a controlled proportion is maintainedbetween the material 23 and the extruded rubber 20. These proportionsare not necessarily constant. The metering of the material 23 may bevariable, the proportion being adjusted as a function of the locationwhere the strip 22 is laid in the tire.

FIGS. 15 and 16 illustrate the result obtained when three complete turnsof a strip 22 wound on a support of revolution such as a rotary coreacting as a manufacturing reference for a tire are superposed. A lack ofhomogeneity (all the greater, the greater the thickness “e” of thestrip) is noted at the azimuth of laying of the start 22A of the strip,which it is quite difficult to mask even by correctly positioning theazimuth of the end 22B of the strip.

In order to overcome this difficulty, it is desirable to be able toeffect starting and ending of laying at a variable strip thickness.FIGS. 17 to 20 illustrate another variant of the invention which makesit possible to achieve precisely that. To this end, the thickness ofsaid wall of the rubber tube is varied to obtain a variation inthickness of the strip.

It can be seen in FIG. 17 that the ovoid 12B is extended by a tail 18B,mounted in an ad hoc bore on the pre-die 17. The tail 18B penetratesinto a cylinder 182B and ends in a disc 181B forming a piston whichslides in said cylinder 182B. A device for controlling the displacement183B makes it possible to act on the relative position of the tail 18Brelative to the pre-die 17, for example by injecting or withdrawing agiven quantity of oil into/from the chamber 184B. Thus, the position ofthe ovoid 12B within the nozzle 11 (FIG. 18) is adjustable in adirection parallel to the flow of uncured rubber in the air gap.Furthermore, just upstream of the extrusion orifice, the nozzle 11 andthe ovoid 12B have a frustoconical surface. In this manner, by acting onthe relative position of the ovoid 12B in the nozzle 11, the thicknessof the air gap and, consequently, the thickness of the extruded tube ofrubber is varied.

FIG. 18 shows the extrusion of a tube, the walls of which are of athickness such that, once flattened against the support S, a strip ofthickness “e2” is obtained for the position of the ovoid 12B illustratedin FIGS. 17 and 18. In FIGS. 19 and 20, there can be seen anotherposition of the ovoid 12B, further to the inside of the nozzle 11. Inthe configuration of these elements as illustrated, the air gap issmaller. Once the tube is flattened against the support S, a strip oflesser thickness “e1” is obtained. Note that the width of the extrudedstrip, which depends mainly on the diameter “d” of the tube, issubstantially independent of the thickness.

By gradually varying said thickness, of course in synchronization withthe volume extruded and the rotation of the support S, it is possible toobtain a start 22C and an end 22D of the strip which extends over an arcα of greater or lesser size, as illustrated in FIGS. 21 and 22.

The invention has been illustrated for operations of laying the strip ina spiral. The invention is also useful for laying strip in a helix, andmore generally for any form of laying of a rubber product by directextrusion on a support in the manufacture of tires.

1. A machine for laying a component comprising uncured rubber for themanufacture of a tire, said machine winding a band on a rotary support,said machine comprising: an extruder equipped with a die imparting atubular form to the section of extruded uncured rubber, a rotary supportof revolution, serving as a reference for the manufacture of the tire, amanipulating robot which imparts all the desired relative positionsbetween said support of revolution and said die, and at least one rollerdownstream of said die cooperating with the rotary support to flattenthe tubular form on the rotary support.
 2. The machine according toclaim 1, wherein said extruder comprises a piston.
 3. The machineaccording to claim 1, wherein said die comprises a nozzle having anextrusion orifice and an ovoid fastened to said nozzle and partiallyblocking off the extrusion orifice so as to provide an air gap betweenthe nozzle and the ovoid, the air gap ending in an extrusion section. 4.The machine according to claim 3, wherein the ovoid is in a positionwithin the nozzle which is adjustable between a centered position andeccentric positions.
 5. The machine according to claim 3, wherein theair gap has a minimum size upstream of the extrusion orifice.
 6. Themachine according to claim 3, further comprising a pipe which passesthrough the ovoid and opens into the extrusion orifice for introducing amaterial into said tubular form.
 7. The machine according to claim 3,wherein the nozzle and the ovoid comprise a frustoconical surface andwherein the ovoid is in a position within the nozzle which is adjustablein a direction parallel to flow of uncured rubber in the air gap.